Process for the preparation of methyl methacrylate

ABSTRACT

A process for producing methyl methacrylate, which comprises subjecting methacrolein and methanol to direct esterification reaction to thereby obtain a reaction mixture liquid containing at least methyl methacrylate and methanol, adding additional methacrolein to the reaction mixture liquid as an entrainer, and distilling the resulting reaction mixture liquid to recover the methanol.

The present invention relates to a process for producing methylmethacrylate, according to which methanol can be recovered bydistillation from a reaction mixture liquid, which is obtained by directesterification reaction between methacrolein and methanol and whichcontains at least methyl methacrylate and methanol, and the recoveredmethanol can be used as a material for the direct esterificationreaction.

BACKGROUND ART

For recovering methanol by distillation from a reaction mixture liquidcontaining methyl methacrylate and methanol, JP-B-1-47454 proposes aprocess comprising feeding a saturated hydrocarbon having 6 to 8 carbonatoms to a distillation column, thereby separating methanol and thelike.

As a similar process, JP-A-57-9740 proposes a process, in which at thetime when methyl methacrylate is refined by distillation in a mannersuch that a mixture liquid containing methanol, water and methylmethacrylate is fed to a distillation column, a saturated hydrocarbonhaving 6 to 7 carbon atoms is placed at a plate(s) substantially above aplate to which the foregoing mixture liquid is fed, and as a result, thesaturated hydrocarbon and substantially whole amount of methanol aredistilled out from a top of the column and are subjected to separationthrough a phase separation tank, and thereafter the methanol phase issupplied to a second distillation column to recover methanol from abottom of the column.

Further, JP-A-58-180457 discloses that methanol can be separated in amanner such that an entrainer capable of forming an azeotrope withmethanol in the presence of methyl methacrylate and water is added to amixture containing methanol, water and methyl methacrylate, followed byazeotropic distillation, thereby a mixture of the entrainer and methanolis obtained from a top of the column, and, when the mixture forms twophase, these two phases are separated from each other. In said JP-A, inaddition to hydrocarbon solvents such as n-hexane, n-octane,cyclohexane, benzol and toluol, solvents such as diisopropyl ether,tetrahydrofuran and dimethyl carbonate are exemplified as suitableentrainer.

Furthermore, JP-A-7-69948 discloses that methanol is recovered in amanner such that a hydrocarbon solvent and water are added to a reactionmixture liquid to obtain a blend liquid, the blend liquid is separatedinto two phases of an organic phase and a hydrous methanol phase, andthen methanol is separated by distillation from the hydrous methanolphase.

However, according to these processes, in distilling, a large amount ofthe hydrocarbon is added as the entrainer to carry out the azeotropicdistillation, and as a result, the distillation needs a great deal ofutilities. Moreover, when attempting to produce methyl methacrylate byusing the recovered methanol for direct esterification reaction withmethacrolein, it is necessary to separate the entrainer contained in therecovered methanol by means of distillation, extraction or the like, sothat the procedure becomes troublesome.

Besides the foregoing processes, there are processes for recoveringmethanol by distillation of the reaction mixture liquid without use ofany entrainer. However, according to such processes, the recoveredmethanol contains a large amount of the object product of the directesterification reaction, namely methyl methacrylate, and therefore suchprocesses are not efficient.

DISCLOSURE OF INVENTION

Accordingly, an object of the present invention is to provide a processfor producing methyl methacrylate, according to which methanol can berecovered by distillation from a reaction mixture liquid, which isobtained by direct esterification reaction between methacrolein andmethanol and which contains at least methyl methacrylate and methanol,and the recovered methanol is used as a material for the directesterification reaction, wherein any hydrocarbon, which should beseparated and removed later, is not used as the entrainer forsimplifying the procedures when recovering the methanol by distillation,and thereby a content of methyl methacrylate in the recovered methanolcan be reduced.

The present inventors have undertaken extensive studies, and as aresult, it has been found that the above-mentioned problems can besolved by adding additional methacrolein as an entrainer when recoveringmethanol by distillation. Thereby, the present invention has beenaccomplished.

That is, the present invention provides a process for producing methylmethacrylate, which comprises subjecting methacrolein and methanol todirect esterification reaction to thereby obtain a reaction mixtureliquid containing at least methyl methacrylate and methanol, addingadditional methacrolein to said reaction mixture liquid as an entrainer,and distilling the resulting reaction mixture liquid to recover themethanol.

In the present invention, the recovered methanol can be used as amaterial for the production of methyl methacrylate by the directesterification reaction.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, a process for producing methyl methacrylate bydirect esterification reaction between methacrolein and methanol,hereinafter referred to as “direct esterification reaction” for brevity,is not particularly limited, and may be any of a gas phase or liquidphase reaction. How to carry out the reaction is also not particularlylimited, and the reaction may be carried out in any of a continuous orbatch manner. For example, there can be given a process comprisingcarrying out the reaction using a palladium based catalyst in a liquidphase in a continuous manner.

Although the reaction mixture liquid obtained by the directesterification reaction usually contains a non-reacted material and aproduct of methyl methacrylate, a reaction mixture liquid pertaining tothe present invention is that containing at least a non-reacted materialof methanol and a product of methyl methacrylate.

The methanol and methyl methacrylate concentrations in the reactionmixture liquid vary depending upon the reaction conditions and the like.For example, when the reaction is carried out in a liquid phase using apalladium based catalyst, the methanol concentration in the reactionmixture liquid is usually from 25 to 70% by weight, and the methylmethacrylate concentration therein is usually from 20 to 60% by weight.Besides these, the reaction mixture liquid usually contains anon-reacted material of methacrolein, a by-product of methyl formate,water and others.

When it is required to remove low boiling by-products such as methylformate from the reaction mixture liquid, it is permitted to add anoperation before the distillation for the recovery of methanol, whichoperation is carried out, for example, in a manner such that thereaction mixture liquid is fed in advance to a distillation column andthe low boiling by-products are distillation-removed with a part ofmethacrolein and methanol from a top of the column.

In the present invention, in recovering methanol from the reactionmixture liquid by distillation, additional methacrolein is added to thereaction mixture liquid as an entrainer. A process for adding theadditional methacrolein thereto is not particularly limited. Forexample, there are given a process comprising feeding the reactionmixture liquid and the methacrolein to suitable positions of thedistillation column, respectively, and a process comprising adding themethacrolein to the reaction mixture liquid, followed by feeding to thedistillation column. By the distillation, methanol can be taken out froma top of the column together with methacrolein which has azeotropicpoint with methanol.

An addition amount of the additional methacrolein used for such apurpose is preferably from 20 to 200 parts by weight, particularlypreferably from 40 to 80 parts by weight based on 100 parts by weight ofthe methanol contained in the reaction mixture liquid. When the amountof the methacrolein is less than 20 parts by weight, methyl methacrylatemay be distilled out in a large amount at the time of recoveringmethanol, thereby making the recovery of methanol difficult. When itexceeds 200 parts by weight, an excess amount of the methacrolein isrecycled to a reactor, and as a result, the reaction may be adverselyeffected in a manner such that it becomes difficult to control a ratioof the materials of methanol and methacrolein within a suitable range,or methacrolein may be polymerized by itself.

In the present invention, a form of the distillation column used for therecovery of methanol is not particularly limited, and may be aconventional one such as a plate type and a packed type. When the liquidin the column forms two phases, water may be separated and taken outwith use of a decanter. Although the distillation conditions are notparticularly limited, it is preferred to apply normal pressure orreduced pressure as distillation pressure and a temperature of nothigher than 120° C. as a column bottom temperature to inhibit anypolymerization.

In the present invention, the methanol recovered by distillationcontains methacrolein. Methanol and methacrolein concentrations in therecovered methanol vary depending upon the reaction mixture liquid to bedistilled, operation conditions of the distillation and the like. Themethanol concentration is usually from 30 to 70% by weight and themethacrolein concentration is usually from 20 to 70% by weight.

The thus recovered methanol can be used as a material for the productionof methyl methacrylate by direct esterification reaction as it is. Inusing it as a material for the production of methyl methacrylate bydirect esterification reaction in the original reactor or anotherreactor, usually methanol and methacrolein are suitably added to adjustto desired material concentrations or desired amounts to be fed.

The present invention is explained with reference to Example andComparative Example as follows. The weight compositions of the reactionmixture liquid and the like were analyzed by means ofgas-chromatography.

EXAMPLE 1

In a 4 liter reactor equipped with a condenser and a stirrer, 350 g of acatalyst (a calcium carbonate catalyst containing 5% by weightpalladium-1% by weight lead-1% by weight iron) and a reaction liquid of700 g of methacrolein and 1280 g of methanol were charged, and thereaction was continued for 4 hours at a bath temperature of 80° C. underpressure of 400 kPa·abs, while blowing air and nitrogen at rates of 4.77Nl/min and 5.0 Nl/min, respectively, thereby to synthesize methylmethacrylate. The reaction product was collected and analyzed, and as aresult, a conversion of methacrolein and a selectivity of methylmethacrylate were found to be 75.1% and 85.2% , respectively.

The thus obtained reaction mixture liquid collected was fed to adistillation column having 50 plates, and low boiling materials such asmethyl formate were distilled out from a top of the column. The reactionmixture liquid, after such distillation, was found to have a compositioncomprising 32.1% by weight of methyl methacrylate, 51.1% by weight ofmethanol, 8.8% by weight of methacrolein and 6.4% by weight of water.

Successively, distillation was carried out at a reflux ratio of 2.0under column top pressure of 80 kPa·abs, while feeding said liquid tothe 25th plate of Oldershaw type distillation column having 50 plates at394.7 g/h and feeding methacrolein to the 24th plate thereof at 105.3g/h. As a result, from a top of the distillation column, a distillatecontaining 53.9% by weight of methanol, 37.4% by weight of methacroleinand 7.4% by weight of methyl methacrylate was obtained at 374.1 g/h, andfrom a bottom of the column, a liquid containing 78.8% by weight ofmethyl methacrylate and 16.4% by weight of water, in other words,containing substantially neither methacrolein nor methanol, was obtainedat 125.8 g/h. A partition ratio of methyl methacrylate in the distillateto that of the column bottom liquid was found to be 0.28. Although thedistillate obtained from the column top contains a small amount ofmethyl methacrylate, the distillate could be used without any problem asa material for the direct esterification reaction by supplying methanoland methacrolein.

COMPARATIVE EXAMPLE 1

Distillation was carried out to recover methanol in the same manner asin Example 1 except that no methacrolein was fed to the distillationcolumn. As a result, from a top of the distillation column, a liquidcontaining 72.0% by weight of methanol, 12.3% by weight of methacroleinand 14.7% by weight of methyl methacrylate was obtained at 280.0 g/h,and from a bottom of the column, a liquid containing 74.7% by weight ofmethyl methacrylate and 20.1% by weight of water, in other wordscontaining substantially neither methacrolein nor methanol, was obtainedat 114.7 g/h. However, a partition ratio of methyl methacrylate in thedistillate to that of the column bottom liquid was found to be 0.48,which was larger than that in Example 1.

INDUSTRIAL APPLICABILITY

According to the present invention, methanol can be recovered bydistillation from a reaction mixture liquid, which is obtained by directesterification reaction between methacrolein and methanol and whichcontains at least methyl methacrylate and methanol, the procedure can besimplified when the recovered methanol is used as a material for thedirect esterification reaction, and a content of methyl methacrylate inthe recovered methanol can be reduced, so that the object product ofmethyl methacrylate can be efficiently produced.

What is claimed is:
 1. A process for producing methyl methacrylate,comprising esterifying a mixture comprising methacrolein and methanol toform a reaction mixture liquid comprising at least methyl methacrylateand methanol, adding additional methacrolein to said reaction mixtureliquid, and distilling the reaction mixture liquid to recover themethanol.
 2. The process according to claim 1, further comprisingesterifying a mixture of the recovered methanol and methacrolein.
 3. Theprocess according to claim 1, wherein the additional methacrolein isadded to the reaction mixture liquid during distilling.
 4. The processaccording to claim 3, wherein the additional methacrolein is added in adistillation column.
 5. The process according to claim 1, wherein theadditional methacrolein is added to the reaction mixture liquid beforedistilling.
 6. The process according to claim 1, further comprisingdistilling low boiling materials from the reaction mixture liquid beforeadding additional methacrolein.
 7. The process according to claim 1,wherein esterifying includes contacting the methacrolein and methanol inthe presence of a catalyst.
 8. The process according to claim 1, whereinthe recovered methanol comprises methacrolein.
 9. The process accordingto claim 7, wherein the recovered methanol further comprises methylmethacrylate.
 10. The process according to claim 1, further comprisingisolating an azeotrope of methanol and methacrolein.
 11. The processaccording to claim 1, wherein the reaction mixture liquid comprises from25 to 70% by weight of methanol and from 20 to 60% by weight ofmethylmethacrylate.
 12. The process according to claim 1, wherein theamount of additional methacrolein added to the reaction mixture liquidis from 20 to 200 parts by weight, based on 100 parts by weight of themethanol in the reaction mixture liquid.
 13. The process according toclaim 1, wherein the amount of the additional methacrolein added to thereaction mixture liquid is from 40 to 80 parts by weight based on 100parts by weight of the methanol in the reaction mixture liquid.
 14. Theprocess according to claim 1, further comprising separating water with adecanter during distilling.
 15. The process according to claim 1,wherein the temperature of the reaction mixture liquid is not higherthan 120° C. during distilling.
 16. A process for producing methylmethacrylate, comprising esterifying a mixture comprising methacroleinand methanol to form a reaction mixture liquid comprising at leastmethyl methacrylate and methanol, adding additional methacrolein to saidreaction mixture liquid, and distilling the reaction mixture liquid torecover the methanol. wherein the methacrolein is added to the reactionmixture liquid during distilling in a distillation column.
 17. Theprocess according to claim 16, wherein the reaction mixture liquidcomprises from 25 to 70% by weight of methanol and from 20 to 60% byweight of methylmethacrylate.
 18. The process according to claim 16,wherein the amount of additional methacrolein added to the reactionmixture liquid is from 20 to 200 parts by weight based on 100 parts byweight of the methanol in the reaction mixture liquid.
 19. The processaccording to claim 16, wherein the amount of additional methacroleinadded to the reaction mixture liquid is from 40 to 80 parts by weightbased on 100 parts by weight of the methanol in the reaction mixtureliquid.
 20. The process according to claim 16, wherein the temperatureof the reaction mixture liquid is not higher than 120° C. duringdistilling.